JP2558317B2 - Video signal processing circuit in disc player - Google Patents

Description

TECHNICAL FIELD The present invention relates to a video signal processing circuit in a disc player.

2. Description of the Related Art In an optical disc player, when an information recording disc (hereinafter, simply referred to as a disc) is warped due to a change with time or the like, the disc is positioned with respect to an optical axis of an information detection light beam emitted from an optical pickup. Since the track pitch between adjacent recording tracks is narrowed equivalently due to the tilt of the information recording surface of, the beam spot diameter on the information recording surface will be affected by the pit information of the adjacent recording tracks. This becomes easier and causes an increase in crosstalk. The influence of this crosstalk appears as a noise component in the video signal reproduced from the disc, which causes deterioration of the image. In order to improve such performance deterioration, conventionally, the inclination of the optical axis of the information detecting light beam with respect to the information recording surface of the disc is detected, and the optical axis of the light beam is always perpendicular to the information recording surface. A so-called tilt servo is performed to adjust the tilt of the pickup so that

FIG. 2 shows the configuration of a tilt servo device that has been conventionally used as a measure against crosstalk. In the figure, an optical pickup 3 for reading recorded information on a disk 2 which is rotationally driven by a spindle motor 1 is an objective lens 4
Is included. The objective lens 4 is attached to an optical system body 5 so as to be movable in the optical axis direction thereof, and is driven by a focus actuator (not shown). The optical system body 5 has the objective lens 4 with respect to the slider base 6.
It is rotatably attached about a rotation fulcrum O located on the optical axis A-A '. The adjusting mechanism 7 including a tilt motor M (shown in FIG. 3) and a speed reducing mechanism rotates the optical system body 5 with respect to the slider base 6, thereby causing the optical axis AA ′ of the objective lens 4. The tilt of the information recording surface is adjusted. The slider base 6 is arranged along a guide rail (not shown) in the radial direction B- of the disk 2.
B'is movable and is driven by a drive mechanism (not shown) including, for example, a slider motor and a reduction gear.

A tilt sensor 8 for detecting a tilt angle of the disk 2 with respect to the optical axis AA ′ is included in a plane including the optical axis AA ′ of the objective lens 4 and perpendicular to the moving direction of the slider base 6. It is provided close to the lens 4. As shown in FIG. 3, the tilt sensor 8 includes one light emitting element 9 and two light receiving elements 10a and 10b.
Reflected light from the information recording surface of the disc 2 based on the light beam emitted from the light receiving element 10a, 10b is received. The difference in the amount of light received by the light receiving elements 10a and 10b is obtained by the differential amplifier 11,
This difference signal is supplied to the tilt motor 13 in the adjusting mechanism 7 (shown in FIG. 2) via the drive amplifier 12 as tilt information with respect to the optical axis AA 'of the disk 2.

In such a configuration, when the slider base 6 moves from the position (a) to the position (b) in FIG. 2 and reaches the inclined portion of the outer peripheral portion of the disk 2, it responds to the drive signal based on the output of the tilt sensor 8. The adjusting mechanism 7 is actuated to rotate the optical system body 5 clockwise about the rotation fulcrum O in the drawing, and the tilt servo is performed so that the optical axis A-A 'is perpendicular to the information recording surface of the disk 2. Is performed.

As described above, conventionally, the influence of crosstalk is removed by correcting the inclination of the pickup 3 by a mechanical structure, but such a structure has a drawback that the structure is complicated and expensive. Further, since the tilt sensor 8 is mounted on the pickup 3, it also hinders downsizing of the pickup 3.

SUMMARY OF THE INVENTION Therefore, according to the present invention, a video signal processing circuit in a disc player which eliminates the problems of structural complexity and cost in a conventional mechanical structure by electrically removing the influence of crosstalk. The purpose is to provide.

The video signal processing circuit according to the present invention changes at least one of the attenuation amount, the attenuation band, and the attenuation frequency characteristic of the noise reduction circuit for removing the noise component contained in the reproduced video signal according to the disc radial position of the information detection point. As a result, the noise component due to the crosstalk is removed.

Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an example of, for example, an optical disc player provided with a noise reduction circuit according to the present invention.
In addition to a normal video disc on which an FM signal is recorded, a Hi-Fi video disc on which each FM signal of a video signal and an audio signal and a digital audio signal are multiplexed and recorded,
Furthermore, it is possible to play back a composite disc called CDV, which is the same size as a compact disc, in which the digital audio signal is recorded on the inner circumference side and the video FM signal and the digital audio signal are multiplex recorded on the outer circumference side. Is.

In FIG. 1, a disk 2 is rotationally driven by a spindle motor 1, and its recorded information is read by an optical pickup 3. The pickup 3 includes an optical system including a light source such as a laser diode and an objective lens, a photodetector that receives reflected light from the disc 2, and a position control of the objective lens in the optical axis direction with respect to the information recording surface of the disc 2. It has a built-in focus actuator, a tracking actuator for controlling the position of the information detector beam spot (information detection point) emitted from the pickup 3 with respect to the recording track in the disk radial direction, and the like. The moving position of the pickup 3 in the radial direction of the disc is detected by a position detector 15 such as a slider pot.

The RF signal output from the pickup 3 is a bandpass filter (BPF) 20 for video FM, analog audio FM.
The signal is supplied to a signal low pass filter (LPF) 21 and a digital audio EFM signal band pass filter 22. The video FM signal that has passed through the video FM BPF 20 is supplied to the video demodulation circuit 23, demodulated by the video demodulation circuit 23 to become a reproduced video signal, and the noise reduction circuit 24
After that, it becomes a video output. Pass signal of LPF21 is 2.3MHz
And BPF25L and 25R for passing only the 2.8MHz audio carrier component are separated into left and right analog audio FM signals, and each analog audio signal is FM demodulation circuit 26L, 26
It is demodulated by R and becomes the left and right audio outputs. On the other hand, the digital audio EFM signal separated from the reproduced RF signal by the digital audio EFM signal BPF 22 is demodulated by the EFM demodulation circuit 28 to be left and right audio outputs.

The noise reduction circuit 24 is a filter 240 that passes only a signal component in a predetermined band from the reproduced video signal.
And a limiter 241 formed of, for example, a diode that extracts only a noise component from the signal components passing through the filter 240.
An amplifier 242 for adjusting the level of the noise component extracted by the limiter 241 and a subtractor 243 for subtracting the noise component adjusted by the amplifier 242 to an appropriate level from the original reproduced video signal. . In the noise reduction circuit 24, for example, the gain of the amplifier 242 is variable, and the gain increases as it goes to the outer circumference of the disk according to the position information of the pickup 3 in the disk radial direction obtained by the position detector 15. This increases the amount of attenuation of the noise reduction circuit 24.

Here, when the disc 2 has a warp, the warp becomes steeper as it goes to the outer circumference of the disc as is clear from FIG. It will increase as it goes to the outer circumference. Therefore, as described above, by changing the attenuation amount of the noise reduction circuit 24 according to the position of the pickup 3 in the disk radial direction, the influence of crosstalk on the reproduced video signal is reduced to an electric amount according to the crosstalk amount. You can do it. Further, since the disc radial position of the pickup 3 can be continuously detected by the position detector 15 formed of a slider pot or the like, the attenuation amount of the noise reduction circuit 24 can be changed over the entire recording area of the disc.

In the above embodiment, the effect of crosstalk is reduced by changing the attenuation amount of the noise reduction circuit 24.However, the band for noise reduction by the filter 240 may be changed so as to become wider toward the outer circumference of the disk. The same effect can be obtained by providing the amplifier 242 with a frequency characteristic and changing the attenuation frequency characteristic, and it is also possible to change the attenuation amount, the attenuation band and the attenuation frequency characteristic in parallel. is there. Further, although the attenuation amount, the attenuation band and the attenuation frequency characteristic are continuously changed according to the disc radial position of the pickup 3, at least the attenuation amount, the attenuation band and the attenuation frequency characteristic are divided into several stages according to the disc radial position. 1
May be changed.

Further, in the above embodiment, the moving position of the pickup 3 is directly detected by the position detector 15 composed of a slider pot or the like, but the time and address data recorded on the disk 2 (for example, Q data of subcode or It is also possible to read a 24-bit code etc.) and use this as position information.

It should be noted that the present invention is not limited to application to an optical disc, and can be used as a measure for crosstalk in reproducing a magnetic recording disc or an electrostatic recording disc.

As described above, according to the video signal processing circuit of the present invention, at least one of the attenuation amount, the attenuation band and the attenuation frequency characteristic of the noise reduction circuit is changed according to the disk radial position of the information detection point. As a result, since the influence of crosstalk can be electrically removed, the tilt servo that has been used conventionally becomes unnecessary, and the problems such as the structural complexity and cost in the conventional mechanical structure can be easily solved. .

At present, a pickup having a small amount of crosstalk with respect to the tilt of the disc is selected and used. However, by using the video signal processing circuit according to the present invention, the selection criterion can be relaxed, so that the cost of the pickup can be reduced. As a result, the cost of the player can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of, for example, an optical disc player provided with a noise reduction circuit according to the present invention, and FIGS. 2 and 3 are block diagrams of a tilt servo device conventionally used as a measure against crosstalk. Explanation of symbols of main parts 2 …… Information recording disk 3 …… Optical pickup 8 …… Tilt sensor, 15 …… Position detector 24 …… Noise reduction circuit

Claims (1)

(57) [Claims] 1. A video signal processing circuit having a noise reduction circuit for removing a noise component contained in a video signal reproduced from an information recording disc, wherein a position of an information detection point in a radial direction with respect to the information recording disc is detected. A noise reduction circuit in a disc player, characterized in that at least one of an attenuation amount, an attenuation band and an attenuation frequency characteristic of the noise reduction circuit is changed according to position information by the position detection means.